In a multipoint video conference, each participant contributes a video stream to the conference, and each participant receives one or more video streams that provide a view of the conference. A continuous presence video conferencing view attempts to show aspects of multiple video streams contributed to a video conference in order to give each viewing participant an experience of the conference that is more informative than that achieved by viewing a single contributed stream. Choices of which streams to view are often derived from the energy or speaking confidence measurable from associated contributed audio streams.
Where two or more streams are contributed by video conference participants, the individual streams viewed by the participants may be displayed in a number of ways, including overlapping or non-overlapping compositions, with each stream scaled to show an appropriate level of importance and/or detail. In typical applications, levels of audio activity derived from associated audio streams, and/or fixed or dynamically assigned roles assigned to the streams, are used to determine whether each stream should be displayed to video conference endpoints in a composed conference view.
The video distributed to each participant to provide a view of the conference may be encoded by a transcoding multipoint video conferencing unit (“MCU”), and delivered as a single stream showing the content of one or more contributed source streams, or switched from source by a switching MCU, which forwards one or more contributed source video streams as determined by the requirements and capability of the receiving endpoint. In either case, the MCU at the center determines what is provided to the participants of the conference as their experience of the conference.